RU2636653C2 - Optimal inductor device - Google Patents

Abstract

FIELD: electricity.SUBSTANCE: coil (1) for an inductor (6) is comprised of a plain conductor (2), which is reeled in a circle around the centroidal axis (C). The conductor has an electric insulating layer (3), which insulates every turn of a conductor in the winding from the next turns. The shape of the whole winding, which forms the coil (1), is, in fact, a toroidal-core with an elliptical cross-section. The heat conductivity is greater than 1 W/mK, more preferable - greater than 1.2 and the first preference - greater than 1.5. The magnetic core (7) for the inductor (6) is made of the soft magnetic composite material, which is comprised of the metal particles and of the binding material. The noted particles have a size in the range of 1 to 1000 mcm. The particles with a size of more than 150 mcm are covered with the ceramic surface with a view to ensuring the electric insulation among them. The magnetic metal particles' volume ranges from 0.5 to 0.9 to the core overall volume. The inductor (6) comprises the coil (1) and the core (7). Basically, all the noted particles in the core are magnetically leveled up with the coil magnetic field. The coil (1) and the core (7) production technique is described.EFFECT: reliability growth and decrease in dimensions.12 cl, 3 dwg

Description

Field of Invention

The present invention generally relates to the design of an optimal inductor. More specifically, the present invention relates to a coil for an inductor, as defined in the restrictive parts of claim 1, a core for an inductor, as defined in the restrictive parts of claim 6, and an inductor comprising said coil and said core, as defined in the restrictive parts paragraph 8 of the claims. The invention further relates to a method for manufacturing said coil and said core, as defined in the restrictive parts of claims 13 and 15.

BACKGROUND OF THE INVENTION

In the ever-growing power electronics industry, inductors are becoming increasingly important in applications such as power generation, power quality, AC drives, feedback drives, etc. Inductors are often key components in the equipment used and often determine the efficiency and productivity of the equipment in question. A particularly problematic area has become applications in which the inductor must simultaneously process the fundamental frequency of, for example, 50 Hz, at the same time, filtering out higher frequencies of the final signal generated, for example, by switching power supplies. Similarly, power electronics is often a source of harmful non-linear distortions, which today have become one of the most important problems of the electric power quality industry.

Conventional inductors, as a rule, are made either by winding wires on a coil frame, in air or on an iron (solid, laminated or ferrite) core. The wire is then wound around a core, which typically has an air gap to control permeability, so as not to saturate the core material. This becomes a source of magnetic flux, energy loss and heating of the surrounding metal. If the coil is wound through air gaps, significant edge losses will often occur, resulting in hot spots that can be difficult to cool. In addition, inductors typically have standardized coil cages, conductor and core materials. This inevitably leads to restrictions on the freedom of design, as a result of which there are inefficient and non-optimized designs of inductors.

The first step towards eliminating or mitigating the above drawbacks has appeared in the last ten years, with the advent of new materials technology. This new material technology provides the best opportunity to specifically adapt, optimize, and integrate these types of power drives in consumer products as well as industrial products. The technology of materials under consideration is composites of soft magnetic materials with a varying amount of binder and filler, called soft magnetic composites (SMC). The formation of these components made of SMC is of great interest, since the needs for a high degree of compaction of the metal and freedom of design are in conflict with the known manufacturing methods, especially in terms of production costs. A successful molding process will result in an inductive component, which in many ways surpasses the usual ones in terms of lower losses, smaller size, providing closer integration into the final device / product.

In addition, many shortcomings are still inherent to inductors, depending on the choice of materials, based on energy losses, thermal deficiencies and shortcomings of hot spots, annoying sound caused by strong currents at sound frequencies, excessive and inefficient use of materials, lower efficiency at higher frequencies and saturation at low flow rates, etc.

The use of inductors in industry is constantly growing, and the demand for more productive inductors is growing along with the need. In addition, high performance inductors are relatively expensive. Thus, there is a need for a new and improved inductor having improved performance in light of the above disadvantages. The improved performance of advanced inductors should preferably be implemented in a cost-effective manner.

SUMMARY OF THE INVENTION

The aim of the present invention is to improve the current state of the art to eliminate the above drawbacks and provide an improved inductor with improvements to both its coil and core. These and other goals are achieved by a coil consisting of a metal wire wound in a circle around a central axis (C), the wire having a layer of electrical insulation that insulates each turn of the wire in the winding from adjacent turns, the shape of the entire winding making up the coil is essentially toroidal having a substantially elliptical cross section and has a bulk thermal conductivity above 0.8 W / m * K.

Thermal conductivity and shape are obtained using a compression device, which significantly reduces the air or gas voids present in the coil, reducing energy loss, and increases the compactness of the coil. The compactness of the coil in combination with the toroidal shape increases the magnetic field of the coil, which is especially important for smaller inductors, where a proper magnetic field is preferred to generate the required flow in the core material.

The coil having a toroidal shape is preferably an annular torus having a substantially circular cross section. This is an additional step in optimizing the magnetic field with respect to the weight and size of the coil used.

The coil should preferably additionally have a thermal conductivity higher than 1 W / m * K, more preferably higher than 1.2, even more preferably higher than 1.5, and most preferably higher than 2. Higher thermal conductivity is obtained, inter alia, due to the large volume metal relative to the total volume in the twisted coil, also called the fill factor, and by reducing air and gas voids and replacing them, for example, with an insulation material and a resin with a higher thermal conductivity than air or gas, at the same time, as before mu having sufficient electrical isolation between each turn in the winding. High thermal conductivity is necessary so that the heat created by losses in the coil during operation can easily reach the outer surface of the coil and, as a result, the outer surface of the inductor. The lower temperature of the coil is not only useful for the overall performance of the coil, but it is necessary to achieve higher performance efficiency, as well as to preserve the properties of insulating materials, thereby increasing its service life. In order to obtain a high fill factor, the cross section of the winding wire in each position is preferably shaped so as to fit snugly against adjacent turns of the wire in the winding, substantially reducing voids in the winding. By eliminating voids in the winding, the risk of breakdown of the dielectric by a partial discharge is significantly reduced. The cross-sectional shape of each individual wire in the coil can be predominantly hexagonal, since it is a natural form when several rounded wires are compressed lying close to each other, as is the case when a rounded wire is wound and compressed to remove air or gas voids. This does not apply to the outer layer of wires, which is given the optimal shape in accordance with the round outer shape of the entire coil, when viewed in cross section. The conductive material used for the coil can be any material suitable for use for the coil, preferably copper or aluminum.

An insulating layer that insulates parts of the wire from adjacent parts of the wire, i.e. the insulating coil of wire from the next coil of wire is preferably a material made of electrical insulating paper and / or resin. Insulating paper can be wound around the wire and saturated from the inside with semi-cured or unbaked resin present on the wire and / or its cores, as explained below. The resin is then cured, for example, by heat. However, the insulating layer may be any suitable electrical insulating material with sufficient insulating properties to produce a thin layer, while maintaining sufficient dielectric and capacitive insulation properties between the turns.

A wire may consist of one or more separately insulated conductors, depending on the total current and its frequency. With smaller cores, the losses associated with surface effects will be reduced.

The cross section of each core in each position has such a shape that it fits snugly to adjacent wires, reducing voids in the wire, which is important for optimizing the magnetic field and thermal conductivity of the coil. Also, this cross section, as for the wire as a whole, is preferably hexagonal, since this is natural when compressing the cores of circular cross section to eliminate any gaps between them. This does not apply to the outer core layer, which is given the optimal shape according to the round outer shape of the entire wire.

In cases where the wire constituting the coil contains several cores, the bundle of cores is optimally bent by approximately 360 °, ± 90 °, for the entire winding of the coil, thereby significantly reducing the proximity effects caused by higher frequencies in the coil. By using the essentially parallel aforementioned cores, a simple litzendrat is obtained in a cost-effective manner. The cores are preferably electrically insulated with a cured resin and a non-baked resin, as explained below. Electrical insulation is very thin compared to the cross section of the cores and can be a thin polymer coating, a thin layer of resin, etc. Since each core has a similar, optimally equal, potential, insulation does not have to be very thick.

Using one or more layers of unbaked resin on the core insulation, it is possible to solidify the resin in the coil forming device and then maintain the optimal shape of the coil after unloading it from the shape of the device. The coil is first heated to the required temperature level to substantially harden the unbaked layers of resin on the cores. Unbaked resin also flows into the air cavities inside the coil, reducing hot spots in the coil, improving heat-conducting properties. In addition, an unbaked resin improves the dielectric and capacitive leakage properties of external electrical insulating paper that can be used around each whole wire.

Outside the coil, in order to further improve the electrical insulation, a third insulating layer must be attached to the soft magnetic core material to be formed on the coil. It is important that this insulation ensures that no core particles are in direct contact with the conductive material, in order to avoid a dielectric short circuit either between the wires or from the coil to the core material. To achieve this, saturation of the electrical insulating resin material is preferred. This third insulating layer also provides a flat or smooth outer surface, so that localized high-intensity B-streams that create hot spots are eliminated. It also reduces capacitive leakage to the soft magnetic core and ground if the core material is grounded.

The objectives of this invention are further achieved by using a magnetic core, for example, for an inductor, wherein the core is made of a soft magnetic moldable composite (SM2C) material made of metal particles and a binder, said particles having a size in the range from 1 μm to 1000 μm, a certain part of the particles, i.e., larger than 150 microns, is covered with a ceramic surface to provide electrical insulation between the particles, and the ratio of the filler of magnetic metal particles to the total volume mu core is from 0.5 to 0.9.

The core can be molded, and therefore it is suitable for embedding coils in it. The molding process makes it possible to obtain good thermal interaction between the core and the coil by eliminating air or gas voids between the coil and the core. The binder may be a polymer, for example, an epoxy or ceramic based binder. A core having the indicated volume ratio of the metal filler will have good heat-conducting properties and high volume resistivity due to isolation between the particles. Particle isolation also improves high frequency properties. Since the core is molded, any shape of the core can be obtained.

It is also preferred that the particles have a size of 10 μm to 800 μm, further optimizing the properties of the core and enhancing its magnetic properties. The size chosen to some extent depends on the intended use of the core. Smaller particles give better high-frequency core properties.

The metal particles may have a composition consisting of: 6.5-7.5% Si, preferably 6.8-7% Si, and the remaining particles are composed of Fe. The powder can be made using gas atomization, giving its particles an almost spherical shape. The metal particles may also have a composition consisting of: 8-10% Si, preferably 9% Si; 5-7% Al, preferably 6% Al; and the remaining particles are composed of Fe.

Another objective of the present invention is the provision of a method of manufacturing a magnetic core, comprising the steps of: placing a soft magnetic composite material made of metal particles and a binder material in a mold, and creating a magnetic field in the mold during the molding and / or curing phase of the material, magnetic alignment core particles with a magnetic field. A magnetic field during production is preferably obtained by placing the coil in shape and conducting current through the coil. An important feature of the core is that the particles in the SM2C material are aligned with the magnetic field of the intended use of the core. Therefore, it is preferable to use the magnetic field for which the core is manufactured, i.e. in the case of manufacturing an inductor, a coil is preferably used to induce a magnetic field during production. If the core is used for another application, the magnetic field can be induced in other ways.

The objectives of the present invention are further achieved by using an inductor, characterized in that the coil described above is embedded in the core, as described above, and the coil has an electrical insulating layer covering its surface area, and substantially all of these particles in the core are magnetically aligned with magnetic field created by the coil.

The combination of an improved coil as described above with an improved core as described above results in an optimal inductor design. The coil is optimally shaped and optimally designed, and can be fitted to the core of the optimal shape, since the core can be molded in any shape. The optimal shape for the core is the toroidal shape that covers the coil. The B-stream is then evenly distributed, and losses due to the high-intensity stream are reduced. In addition, the core material is used optimally, removing excess material that affects the size and weight of the inductor. The absence of voids in the structure, which creates a direct thermal interaction between the core and the coil, is an additional reason for eliminating hot spots in the core material, which at the same time optimizes thermal conductivity by transferring heat from the coil and core to the external environment surrounding the inductor.

The presence in the core of particles aligned with the magnetic field, which is induced by the current flowing through the coil, further improves the performance of the inductor, increasing conductivity and reducing losses. Magnetically aligned particles are obtained by conducting current through a coil prior to and / or during the core forming and curing phase. The magnetic field induced by the coil causes forces on the particles in the core, so that they align with the magnetic field.

It is also preferable that the coil is located in the optimal position to ensure essentially the same B-flow in the core material in all directions when viewed from the surface of the coil (same volume in all directions), due to the same core cross-sectional area on the inside of the coil in the direction of the central axis, as on the outer side of the core, when viewed in cross section along a plane perpendicular to the central axis (C) through the center of the coil. The core material will then have an equal and uniform B-stream, which optimizes the loss properties in the material. In addition, the core material is used optimally, removing excess material that affects the size and weight of the inductor. The distance from the coil to the radial outer edge of the core (in a direction perpendicular to the coincident central axis of the toroidal shape of the core and coil) is less than the distance from the coil to the radial inner edge of the core to provide the same core volume on the radial inner side of the coil as on the outer side.

The coil can be further offset from the indicated optimum position to provide a stronger magnetic flux towards the center of the inductor from the coil than towards the periphery of the inductor. This reduces the scattering fields created by the inductor, and also reduces the need for small mechanical tolerances during the manufacture of the inductor. The core may further comprise surface-enhancing elements that change the essentially toroidal shape to increase surface area. The surface-increasing elements may be ribs or ripples on the surface of the core, turning the outer surface of the core into a heat sink. An additional feature of the present invention is a method for manufacturing a coil according to the above-described coil, comprising the steps of applying an insulating layer to a wire, winding the wire around a central axis (C), compressing the winding into an annular torus having a circular cross section, using a compression device, insulating the entire coil from the outside electrical insulating paper and saturating the entire coil with electrical insulating resin. The compression of the wire will adapt to the wire, thereby filling the voids in the winding, increasing the performance of the inductor. Compression can additionally lead to plastic deformation of the conductive material. Adapting the wire together with plastic deformation makes it possible to give the coil a preferred shape and obtain the desired thermal conductivity. The winding is preferably compressed using isostatic pressure above 65 MPa to substantially remove voids in the coil and obtain the desired shape.

During this compression, a current may be additionally applied to the wire. The heat from the current flowing through the coil will solidify the layers of unbaked resin on the wire insulation, making it possible to maintain the optimal shape of the coil after the compression step. Unbaked resin also acts to improve the electrical insulation properties of electrical insulation paper, which can be placed on each wire.

An additional feature of the present invention is a method of manufacturing a magnetic core, in which current is conducted through the coil before and / or during the phase of molding and / or curing of the material, magnetically aligning the core particles with the magnetic field of the coil. This alignment further improves inductor performance, increasing permeability and reducing losses.

An inductor made with an essentially toroidal coil in SM2C mold (Soft Magnetic Moldable Composite) has several advantages.

Due to the moldable soft magnetic core, geometric features may be optimal with respect to the permeability of the soft magnetic core. The greatest technical benefit of this design is that it provides an almost optimal theoretical flow path for the electromagnetic field in the inductor, avoiding unnecessary angles that create hot spots, shortening the life of the insulating material, and creating losses in the inductor. It is also compact and uniform with good heat distribution and dissipation properties. The toroidal shape of the coil also provides the highest degree of induction for these properties of the core material, since angles lead to localized saturation. The high degree of compactness of the toroidal coil, as described above, further enhances the magnetic field, essentially making it possible to obtain a significantly finer inductor, reducing the need for materials, providing smaller, lighter, more cost-effective elements with higher thermal conductivity.

The use of SM2C core material is a key idea of the invention. It provides a simple production step for forming / creating an optimal toroidal core shape, eliminating unnecessary material outside the flow path. Direct thermal interaction between the coil and the core material, provided by molding the material directly on the surface of the insulated coil, makes it easy to distribute the heat losses generated in the winding to the outer surface of the inductor, where they can be released. At the molding stage, in addition, if necessary, it is easy to create cooling ribs or ripples to further improve the cooling characteristics of the inductor.

A brief description of the graphic materials

The above objectives, as well as additional objectives, features and advantages of the present invention will be more fully understood with reference to the following explanatory and non-limiting detailed description of preferred embodiments of the present invention, taken together with the accompanying graphic materials on which:

FIG. 1 is a perspective view of a coil for an inductor;

FIG. 2a is a cross-sectional view of the coil of FIG. one;

FIG. 2b is an enlarged cross-sectional view of the view shown in FIG. 2a showing core wires;

FIG. 3 is a perspective view of an inductor comprising a coil according to FIG. 1 and FIG. 2 embedded in the core according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a perspective view of an inductor coil 1. The coil 1 has the shape of a torus and consists of a wound wire 2, which is better seen in the cross section of the coil shown in FIG. 2a. The coil is coated or wrapped with an insulation layer 11. In FIG. 2a, it can be seen that the wire 2 has an insulation layer 3 and that the turns of wire in the coil 1 are compressed so that the shape of each inner turn of the wire is hexagonal, filling essentially all of the space, so that the voids are essentially filled. FIG. 2a further shows that the outer layer of the wire of the coil is formed according to the desired toroidal shape of the entire coil, so that the outer layer of the wire repeats the smooth toroidal shape of the torus of coil 1. FIG. 2b is an enlarged cross-sectional view of the view shown in FIG. 2a, showing cores 4 of a wire 2. Cores 4 of a wire 2 are coated with a thin layer 5, for example, of polymer or resin to isolate the cores from each other.

FIG. 3 is a perspective view of an inductor 6 comprising a coil 1 according to FIG. 1 and FIG. 2a, b embedded in the core 7 according to the present invention. You can see the ends 8, 9 of the wire, which is wound on a coil 1. The ends 8, 9 are used to connect the inductor during operation of the inductor. The core 7 has a surface that is shaped like a heat sink 10 to increase the surface and thus increase the heat sink properties of the inductor. In FIG. 3 it is also seen that the distance from the coil in the core is not centered, which is seen in the cross section of the core. The distance D2 of the core material from the coil to its central edge is greater than the distance D1 from the coil to the peripheral edge of the core. Thus, on the central side of the coil, there is essentially the same volume of core material as on the outer side of the coil (away from the central axis of the inductor).

The invention will now be described in detail to explain the function of the optimal design of the inductor.

Coil

The coil consists of separately insulated cores of, for example, copper or aluminum. The electrical insulation on each core is very thin compared to the total cross-sectional area of the core and may consist of, for example, a thin polymer coating. This provides a high fill factor of the conductive material while maintaining low losses from surface effects at high frequencies.

The cores piled together form a wire. A wire may consist of one core or many wires, depending, inter alia, on the total current and its frequency spectrum. With decreasing core diameter, losses associated with surface effects and losses associated with substitution effects will decrease.

By folding all the cores in parallel and then bending the bale with approximately one complete turn (360 degrees, ± 90 °) onto the coil, the substitution effect will be significantly reduced. However, if the veins are turned too tightly, this will negatively affect the fill factor of the wire and create likely damage to the insulation coating when pressure is applied to the coil.

A layer of electrical insulation should be attached around each whole wire. The insulation layer on the wire must be strong enough to withstand mechanical pressures, such as, for example, as a result of winding the wire to form a coil of many turns in the shape of a torus. This material prevents dielectric short circuit between wires and prevents capacitive leakage from wire to wire. To further improve the properties of the coil, especially thermal conductivity and fill factor of conductive materials, the coil can be compressed. Using one or more layers of unbaked resin on the core insulation, the resin can be cured in the coil forming device and then the optimal shape of the coil can be maintained after it is unloaded from the shape of the device. The coil is heated, for example, by passing a strong current through the coil, so that the unbaked resin flows into the air cavities between the cores and wires, improving thermal conductivity, dielectric properties and capacitive leakage properties.

An additional third insulation layer 11 is also attached to the outside of the coil to isolate the coil from the external environment, in this embodiment a molded core. This ensures that the insulation layer covers the entire coil; resin is used in the insulation layer. The resin also makes the outer surface of the coil smooth, repeating the shape of the torus of the coil and adapting well to its magnetic field, thereby avoiding hot spots.

Soft magnetic core

The soft magnetic core that is molded around the coil also has a substantially toroidal shape. The core shape may also be provided, for example, with mounting holes and heat sinks, as shown in FIG. 3.

In fact, the toroidal shape of the core takes advantage of existing technologies to optimally use the exact amount of core material, eliminating any excess material that is redundant / unnecessary for the coil flow path and optimal operation of the inductor. This reduces material costs as well as the weight and size required for the inductor.

The permeability of the SM2C can be adjusted to adapt to the design. By conducting current through the coil during the molding and solidification phases of the material, its permeability can be increased by 10-15%. Then the magnetic field of the coil optimally aligns the surrounding powder particles in the same or similar direction as the magnetic flux lines of each individual element. Maintaining current during curing ensures that the particles maintain their changed and optimized position. This creates an easier flow path for the flow, which increases inductance and reduces inductor losses.

The core is preferably arranged in an axial symmetrical position such that the area of the core material perpendicular to the flow lines is more or less the same in all parts of the inductor.

The particle size distribution is chosen so as to ensure good powder placement in combination with optimized static and dynamic magnetic properties.

To avoid electrical conductivity from particle to particle in the core, the particles are coated with a thin insulating layer before the molding process. The insulating layer can, for example, be made of ceramic nanoparticles, which increases the volume resistivity of the molded core and thus reduces the high frequency induced eddy currents.

Claims (22)

1. The coil (1) for the inductor, consisting of a metal wire (2), wound in a circle around a central axis (C), characterized in that the wire has a layer (3) of electrical insulation that insulates each turn of the wire in the winding from adjacent turns, wherein said wire (2) contains one or more electrically isolated conductors (4), while several conductors (4) are optimally bent by approximately 360 ± 90 ° for a full twisted coil, the shape of the entire winding constituting the coil (1) is essentially toroidal, having an essentially elliptical cross section in a plane perpendicular to the direction of winding of the wire, and the wound coil has such a duty ratio, i.e. the ratio of the volume of the metal to the total volume so that the thermal conductivity of the coil exceeds 0.8 W / (m · K). 2. The coil according to claim 1, characterized in that the toroidal shape is an annular torus having a substantially circular cross section. 3. The coil according to claim 1, characterized in that the cores (4) are electrically isolated by a cured resin or a cured and unbaked resin (5). 4. Coil to any one of paragraphs. 1-3, characterized in that the cross section of each core (4) in each position has such a shape as to fit snugly to adjacent cores, significantly reducing voids in the wire. 5. An inductor (6) containing a coil (1) according to any one of paragraphs. 1-4, and the specified coil (1) is embedded in the core (7), wherein the core (7) is made of a soft magnetic composite material made of metal particles and a binder, wherein the coil (1) has an electrical insulating layer (11) covering its surface area, and the core particles are magnetically aligned with the magnetic field of the coil. 6. The inductor according to claim 5, characterized in that the core (7) has a toroidal shape covering the coil. 7. The inductor according to claim 5, characterized in that the coil (1) is located in the optimal position to ensure essentially the same magnetic flux in the core material in all directions, when viewed from the surface of the coil (the same volume in all directions), due to to a significant extent the same cross-sectional area of the core on the inner side of the coil in the direction of the central axis as on the outer side of the core, when viewed in cross section along a plane perpendicular to the central axis (C) s center of the coil. 8. The inductor according to claim 7, characterized in that the coil (1) is offset from the indicated optimal position, providing a stronger magnetic flux from the coil in the direction toward the center of the inductor than towards the periphery of the inductor. 9. The inductor according to any one of paragraphs. 5-8, characterized in that the core (7) contains surface-increasing elements (10), significantly changing the toroidal shape to increase the surface area. 10. A method of manufacturing a coil (1) according to any one of paragraphs. 1-4, comprising the steps of: applying an insulating layer to the wire (2), winding wires (2) around a central axis (C), compressing the winding into the shape of an annular torus having a circular cross section using a compressing device. 11. A method of manufacturing a coil (1) according to claim 10, characterized in that a current is supplied to the wire (2) during compression. 12. A method of manufacturing an inductor according to paragraphs. 5-9, comprising the steps of: placing a soft magnetic composite material made of metal particles and a binder in a mold, and creating a magnetic field in the mold during the molding and / or curing phases of the material, magnetic alignment of the core particles with the magnetic field.

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